This invention relates to a C-shaped or X-shaped welding gun apparatus having mounted thereon a transformer.
The welding gun apparatus can largely be divided into two kinds; one is the C-shaped welding gun apparatus and the other is the X-shaped welding gun apparatus.
The C-shaped welding gun apparatus generally comprises a gun bracket, a pressurizing cylinder which is slidably supported on the gun bracket, a movable gun arm which is mounted on a piston rod which extends forwards from the pressurizing cylinder, a stationary gun arm which extends from the side of the pressurizing cylinder towards a front of the movable gun arm so as to lie opposite to a front portion of the movable gun arm, and a transformer which is provided on a rear side of the stationary gun arm.
In this kind of C-shaped welding gun apparatus, the following construction is disclosed in the Japanese Published Unexamined Utility Model Application No. 108582/1990. Namely, the construction is characterized in: that a center tap of a secondary coil of a transformer is connected to a movable gun arm through a feeder relay member and a copper-base alloy plate called an ounce metal plate; that a rear end portion of a stationary gun arm is inserted into a pair of terminal plates with a rectifier interposed between the rear end portion and each of the terminal plates, the terminal plates being connected to both ends of the secondary coil of the transformer and being oppositely disposed in the widthwise direction of the transformer; that both terminal plates are pressingly held or sandwiched between a pair of holding plates which are provided on oppositely external sides of both terminal plates, by means of tightening bolts which extend across the holding plates; and that the rear end portion of the stationary gun arm is thus fixedly pressed between both terminal plates with the rectifiers interposed therebetween so that the stationary gun arm is supplied with electric power directly from the rectifiers. In this construction, the above-mentioned terminal plates are symmetrically disposed on both sides of the widthwise center line of the transformer. The stationary gun arm is arranged to extend from between both terminal plates forwards along the center line of the transformer. On one side of the stationary gun arm the above-mentioned ounce metal plate is disposed so as not to contact the stationary gun arm.
The X-shaped welding gun apparatus generally comprises a gun bracket, a pair of gun arms which are rotatably supported by a common supporting shaft which is provided on the gun bracket, and a pressurizing cylinder for opening and closing both gun arms. In case the X-shaped welding gun apparatus is to be equipped with a transformer, the construction in general is that the transformer is supported on the gun bracket, and that one of the feeder terminals and the other of the feeder terminals of the transformer are respectively connected to one of the gun arms and the other thereof via respective ounce metal plates. In this apparatus, there is a disadvantage in that a space is required for laying out the ounce metal plates in a roundabout manner, thereby making the apparatus large in size. In order to eliminate this disadvantage, the following construction is also disclosed in the Japanese Published Unexamined Patent Application No. 99489/1985. Namely, the construction is characterized in: that a bush which is electrically insulated from a supporting shaft is externally fit into the supporting shaft; that one of the gun arms is directly and rotatably supported by the supporting shaft and the other of the gun arms is rotatably supported by the supporting shaft via the bush; that a pair of feeder terminals of the transformer are electrically connected respectively to the supporting shaft and the bush via a respective feeder bar so that electric power is supplied to one of the gun arms via the supporting shaft and to the other of the gun arms via the bush.
In the above-mentioned conventional C-shaped welding gun apparatus, the stationary gun arm is disposed in the widthwise center of a front projected area of the transformer. As a result, the ounce metal plate to be disposed on one side of the stationary gun arm protrudes outside the above-mentioned projected area and, therefore, the width of the welding gun becomes large. This brings about a disadvantage in that this large width becomes a hindrance in inserting the welding gun into a widthwise narrow dented portion to carry out the welding of a workpiece.
In addition, in the above-mentioned conventional X-shaped welding gun apparatus, there is provided on a shaft end side a connecting portion which includes contactors so that each of the feeder bars is connected via each of the contactors to the supporting shaft and to the bush, respectively. This connecting portion protrudes towards the side of the bracket, resulting in a large width of the welding gun. This large width becomes a hindrance to the welding in a narrow place like in the aobve-mentioned conventional C-shaped welding gun apparatus.